Methods for delivering, repositioning and/or retrieving self-expanding stents

ABSTRACT

Methods for delivery and deploying a stent formed of a shape memory alloy to a desired position in a tubular area of the body, and/or for repositioning and/or retrieving a stent formed of a two-way shape memory alloy. An arrangement is provided by which the temperature of the stent is locally adjusted during delivery, repositioning and/or retrieval in a safe and controlled manner by engagement with an expandable and collapsible thermal transfer member situated on a catheter assembly.

FIELD OF THE INVENTION

[0001] The present invention generally relates to advanced medicalendoluminal devices and methods of minimally invasive treatment ofblockages of the blood vessels and other tubular organs. Moreparticularly, the present invention relates to methods for delivering,repositioning and/or retrieving self-expanding stents for internalreinforcing of diseased tubular structure and/or for local delivery ofpharmacological or radioactive agents having a beneficial advantage ofreduction of re-stenosis.

BACKGROUND OF THE INVENTION

[0002] Reference is made to a related application entitled Apparatus forDelivery Repositioning and/or Retrieving Self-Expanding Stents filedconcurrently with this application.

[0003] A stent is a generally longitudinal cylindrical device formed ofbiocompatible material, such as a metal or plastic, which is used in thetreatment of stenosis, strictures, or aneurysms in body blood vesselsand other tubular body structures, such as the esophagus, bile ducts,urinary tract, intestines or tracheo-bronchial tree. Referenceshereafter to “blood vessels” and “vessels” will be understood to referto all such tubular body structures. A stent is held in a reduceddiameter state during its passage through a low profile catheter untildelivered to the desired location in the blood vessel, whereupon thestent radially expands to an expanded diameter state in the largerdiameter vessel to hold the vessel open. As discussed below, radialexpansion of the stent may be accomplished by an inflatable balloonattached to a catheter, or the stent may be of the self-expanding typethat will radially expand once deployed from the end portion of adelivery catheter.

[0004] Non-diseased vessels that are stented have a tendency to developmore aggressive intimal hyperplasia than diseased vessels. Intimalhyperplasia is part of the endothelialization process by which the stentbecomes incorporated into the vessel wall as a result of the vessel'sreaction to a foreign body, and is characterized by deposition of celllayers covering the stent. It eventually results in formation of aneointima, which coats the stent and buries it completely in the vesselwall.

[0005] Endothelialization generally improves patency rates and the morecomplete the apposition of the stent to the vessel wall, the moreuniform and optimal is the degree of endothelialization. Of course, afundamental concern is that the stent be deployed in the correct desiredlocation in the vessel as precisely as possible in the first place. Thisis important when delivering radiation or medication to a particularlocation using the stent.

[0006] Therefore, firstly, it is important that a stent be deployed inthe correct desired position in the blood vessel and, secondly that thestent be as completely apposed to the vessel wall as possible.

[0007] Stents fall into one of two categories based on their mechanismof deployment and radial expansion, namely, balloon-expandable stentsand self-expanding stents.

[0008] Balloon-expandable stents (BES) are mounted in their reduceddiameter state on nylon or polyethylene balloons, usually by manualcrimping, while others are available pre-mounted. One example of a BE isshown in U.S. Pat. No. 4,733,665 to Palmaz. BES rely solely on balloondilation to attain the desired expanded configuration or state. Thisenables BES to be deployed in a relatively controlled gradual manner.BES in general have more strength than self-expanding stents andinitially resist deformation as well as recoil. BES behave elasticallybut eventually yield and become irreversibly, i.e. plastically, deformedunder external force. Most BES are less flexible than self-expandingstents and are therefore less capable of being delivered throughtortuous vessels and, when a BES is deployed in a tortuous vessel, itoften straightens the vessel, forcing the vessel to conform to the shapeof the stent rather than vice versa. This generally results in portionsof the stent not being completely apposed to the vessel wall which inturn affects endothelialization and overall patency rate.

[0009] On the other hand, BES can generally be deployed in a relativelyprecise manner at the correct desired location in the vessel since theycan be deployed in a controlled gradual manner by gradually controllingthe inflation of the balloon. This ability to gradually control theexpansion of the stent, along with the fact that BES rarely change theirposition on the balloon during inflation, enable fine adjustments to bemade by the operator in the position of the stent within the vesselprior to stent deployment.

[0010] Self-expanding stents (SES) are formed of braided stainless steelwire or shape-memory alloy such as nitinol and are generally deliveredto desired locations in the body in a reduced diameter state in a lowprofile catheter while covered by an outer sheath which partiallyinsulates the SES from body temperature and mechanically restrains them.

[0011] Nitinol is an alloy comprised of approximately 50% nickel and 50%titanium. Nitinol has properties of superelasticity and shape memory.Superelasticity refers to the enhanced ability of material to bedeformed without irreversible change in shape. Shape memory is theability of a material to regain its shape after deformation at a lowertemperature. These physical properties of nitinol allow complex deviceconfigurations and high expansion ratios enabling percutaneous deliverythrough low profile access systems.

[0012] Superelasticity and shape memory are based on nitinol's abilityto exist in two distinctly different, reversible crystal phases in itssolid state at clinically useful temperatures. The alignment of crystalsat the higher temperature is called the austenite (A) phase; thealignment of crystals at the lower temperature is called the martensite(M) phase. In between is a temperature interval of gradual transitionbetween the A and M phases.

[0013] Under external force, the shape of a nitinol device can begreatly deformed without irreversible damage. Depending on thetemperature at which this external force is applied, superelastic orshape memory effects prevail. In close vicinity to or above thetemperature defining transition into the full A state, superelasticityresults: as soon as the deforming force is released, the deviceimmediately assumes it original shape. When nitinol is deformed at orbelow the lower temperature of the complete M transition, the shapememory effect can be exploited. The device retains its deformed shapeeven after the external force is removed as long as the temperature ofthe environment stays below the temperature of transition into A phase.Only during heating does the device resume its original shape.

[0014] While the shape memory effect is essentially a one-way typephenomena in which shape recovery occurs only upon heating the alloy toa temperature defining transition to the full A phase, by subjecting thealloy itself to a biasing force, i.e. an internal stress formed bydislocations introduced by plastic deformation in the alloy, a two-wayshape memory can be imparted to the alloy so that cooling the alloy willinduce a shape change.

[0015] One type of self-expanding stent is constructed of wire formed ofa shape-memory alloy, such as nitinol, having a transition temperatureof about body temperature, i.e. 37° C. For example, reference is made toU.S. Pat. No. 5,746,765 to Kleshinski et al. The one-way transitiontemperature is the temperature of transformation of a nitinol devicefrom its collapsed state into a filly expanded configuration. The stentis pre-loaded on a low profile catheter by crimping the stent at roomtemperature (at which it can be plastically deformed) onto the catheter.An outer sheath covers the crimped stent and at least partiallythermally insulates the stent as it is delivered to the desiredlocation. Upon reaching the desired location, the sheath is withdrawnand the stent is exposed to body temperature whereupon it is naturallywarmed to body temperature and expands to its expanded diameter state insupporting contact with the vessel wall. In a fully expanded statewithin the human body, the stent is capable of exerting considerableradial force on the surrounding structures, which allows mechanicalopening of the vessel lumen and maintaining its long-term patentcy forfree passage of flow.

[0016] If an alloy is used for which shape recovery occurs above bodytemperature, the SES must be heated after release into the body. Ifshape recovery occurs below body temperature, the device may be cooledduring the delivery to prevent expansion inside the delivery catheter.If shape recovery occurs at body temperature, no heating or cooling isnecessary during the delivery and deployment, provided delivery isrelatively speedy. If, however, a tortuous iliac anatomy or otherinterference delays prompt deployment of a nitinol stent with thesecharacteristics, premature warming to body temperature could causeexpansion in the delivery sheath, increase friction, and interfere withdelivery. In this instance, flushing with a cool solution has beensuggested.

[0017] SES do not require any special preparation prior to deployment.SES behave elastically throughout their lifetime, and do not becomeirreversibly deformed. When deployed, the nominal diameter is purposelyselected to be greater that the diameter of the vessel. Therefore, oncedeployed, an SES exerts continuous outward force on the vessel as ittries to expand to its original dimensions. The ability of an SES tocontinuously exert an outward force on the vessel coupled with thegreater flexibility of SES, generally results in optimal wallapposition, thereby optimizing endothelialization and improving patencyrates. Nitinol self-expanding stents have been designed having goodradial and hoop strength.

[0018] However, while SES are preferable relative to BES in manyapplications with respect to achieving optimized endothelialization andincreased patency rates, currently available methods for delivering anddeploying SES are not entirely satisfactory. It has generally not beenpossible to deploy SES in the correct desired location in a vessel asprecisely as in the case of BES with currently available deliveryarrangements for the reason that the temperature of the SES rapidlyincreases to body temperature upon withdrawal of the outer sheath andtherefore the stent quickly expands into engagement with the vesselwall. Consequently, there is not always enough time to finely adjust theposition of the SES as it quickly expands, and it is not uncommon forthe distal end of an SES, which is exposed to body temperature first,and which therefore expands before the rest of the SES, to engage andbecome attached to the vessel wall in the wrong position and in turninhibit or prevent further adjustments in the position of the SES in thevessel.

[0019] Another drawback in conventional methods for delivering anddeploying SES, as compared to BES, is that during deployment while BESare advantageously pressed against the vessel wall with a relativelylarge outward force by the dilating balloon in the manner of anangioplasty to insure attachment of the BES to the vessel wall, SES mustrely solely on the outward force exerted by the expanding SES to provideinitial attachment. It is common to supplement the SES placement with asubsequent balloon angioplasty, which requires exchange of the stentdelivery system after completion of stent deployment for a ballooncatheter.

[0020] Still another drawback in conventional methods for delivering anddeploying SES is the possibility that when delivery is protracted, theSES is exposed to body temperature inside the delivery system. Thedeployment process can then become more difficult—the device may openabruptly after being freed from the system and may “jump” beyond thetarget as the SE expands during deployment. BES cannot be repositionedor retrieved after deployment and while arrangements have been proposedfor enabling the repositioning and/or retrieval of SES formed of two-wayshape memory material, no practical workable arrangement has beendeveloped.

[0021] A malpositioned stent often requires an additional stentplacement to correct the mistake and achieve the desired results. Thestents will remain in the vessel for the entire life of the patient. Ina high percentage of patients, the stent will become the site ofrecurrent stenosis due to an aggressive neointimal proliferation. Thesepatients require repeated interventions, which often include balloonangioplasty and/or additional stent placement.

[0022] The most striking illustration of these problems is seen incardiac patients. Stents and balloon angioplasty transformed the care ofpatients with heart disease. Each year, about 700,000 patients in theU.S. undergo angioplasty, in which a balloon is used to clear anobstruction in a coronary artery and a stent is deployed to keep itopen. Yet a disturbingly high 15% to 20% of the procedures fail withinsix months, due to the aggressive neointimal proliferation. Thesepatients will often undergo further major treatments, which might berepeated several times.

[0023] The need to be able to reposition and/or retrieve stents from avessel also arises from the fact that heart researchers and stentmanufacturers are developing a new generation of stents that not onlyprop open the vessel, but which deliver drugs to the site of theblockage in an effort to minimize or eliminate neointimal proliferationand keep the vessel open for long periods of time. Studies have shownthat stents coated with a drug called rapamycin, essentially eliminatesre-stenosis. Other medications, such as nitric oxide and paclitaxel orsimilar compounds, also have a potential to prevent proliferation ofscar tissue by killing such cells. One concern is whether the drugsmight work too well, inhibiting not only re-stenosis, but also thenecessary growth of the thin layer of neointima. As previouslydescribed, this thin layer of cells, which grows over the stent,smoothes its surface (similar to a layer of Teflon), so blood cells canflow over it without damaging themselves. A damaged blood cell initiatesa chemical cascade, which results in clot formation. Therefore anexposed bare metallic stent carries a risk of inducing thrombusformation within it.

[0024] The potential of radioactive stents to prevent re-stenosis is anadditional area of active research, since local radiation has been shownto inhibit the growth of neointima and halt the progression ofatherosclerotic disease.

[0025] One can therefore appreciate the benefit of being able toretrieve a stent used for local drug delivery or radiation treatment,after it has achieved its desired effect. This would eliminate potentialrisk of thrombus formation at the site of the exposed bare stent.

[0026] In summary, ideally an optimal stent and associated deliverymethod should possess and combine all the positive traits mentioned sofar in each of the stent categories. The stent should be pre-loaded onthe delivery apparatus and should not require special preparation. Itshould be flexible to enhance apposition to the vessel wall. It shouldprovide a controlled gradual deployment without stent migration toensure deployment of the stent in the correct location. Lastly, in caseof a malpositioned stent, or stent which is deployed for the purpose ofits temporary effect, such as for local drug delivery, the system shouldhave the option of enabling repositioning and/or retrieval of the stent.

[0027] SES can be preloaded on the delivery apparatus, do not requirespecial preparation and are flexible. However, to date, no satisfactorymethod or apparatus is available for obtaining a controlled gradualdeployment of an SES without stent migration, or for repositioningand/or retrieving a SES. While methods have been suggested in the priorart for delivering SES to a correct location in a precise manner and forrepositioning and retrieving SES formed of two-way shape memorymaterial, these prior art arrangements all have drawbacks and have notbeen adopted in practice.

[0028] A method for delivering, repositioning and/or retrieving an SESformed of a two-way shape memory alloy capable of expansion orcollapsing in the radial direction in accordance with changes intemperature is disclosed in U.S. Pat. No. 5,037,427 to Harada et al.According to Harada et al., a stent is made of nitinol alloy trained tohave two-way shape memory. The stent is in an expanded diameter state atabout body temperature and in a reduced diameter state at a temperaturebelow body temperature. In delivering the stent, the stent is mounted inthe reduced diameter state at the distal end of a catheter over aportion of the catheter having a number of side ports. Cooling watersupplied through the catheter flows out from the side hole and isbrought into contact with the stent during delivery to maintain thestent below body temperature and therefore in the reduced diameterstate. When the SES is positioned at the desired location, the supply ofthe cooling water is stopped and the stent is warmed by the heat of thebody and expands into supporting engagement with the wall of the vessel.The catheter is then withdrawn. In retrieving an already-positioned SESusing this system, the distal end portion of the catheter is insertedinto the expanded stent lumen and a cooling fluid is introduced into thecatheter and discharged through the side ports at the distal end regioninto the vessel whereupon the stent is cooled and purportedly collapsesonto the distal end portion of the catheter. The stent is retrieved bywithdrawing the catheter. The patent suggests that the position of thestent can also be changed using this technique.

[0029] U.S. Pat. No. 5,746,765 to Kleshinski, Simon, and Rabkin alsodiscloses a stent made from an alloy with two-way shape memory, whichexpands inside the vessel due to natural heating to body temperature.The stent is covered with an elastic sleeve. When the metal frame issoftened by decreased temperature, the sleeve overcomes its radial forceand promotes its further contraction for easier retrieval.

[0030] However, in both the arrangements disclosed in Harada et al. andKleshinski et al., a substantial amount of very cold solution must beinfused into the vessel in order to reduce the local temperature of theenvironment surrounding the stent. Cold temperature around the stentmust be maintained for some time until the stent is delivered orrecovered for retrieval or repositioning. This technique appears to beclinically impractical and not safe due to high risk of potential tissueand blood cell damage.

[0031] U.S. Pat. No. 6,077,298 to Tu et al. discloses a retractablestent made from a one-way shape-memory alloy, such as nitinol, that canbe deployed into the body by means of dilation with a balloon catheter.For the stent retrieval, a radio frequency current within the range of50 to 2,000 kHz must be applied directly to the stent to provide partialcollapse of the stent after it is heated to a temperature above 43° C.to 90° C. However, if the transition temperature of the stent materialis in the range of 43° C. −90° C., the radial force of the device willbe greatly reduced at the body temperature of 37° C., and may not besufficient for therapeutic effect. Heating of the stent to almost aboiling temperature can cause irreversible damage to vascular wall andblood coagulation.

[0032] U.S. Pat. No. 5,961,547 to Razavi, U.S. Pat. No. 5,716,410 toWang et al., U.S. Pat. No. 5,449,372 to Schwaltz et al. and U.S. Pat.No. 5,411,549 to Peters disclose temporary or retractable stents in theshape of a spiral coil or a double helix. Although these stents are madeof different materials, such as metal or plastic, and have differencesin the techniques of their deployment (heat-activated, self-expanding orballoon expandable), as well as methods of their retrieval (mechanicalstraightening vs. softening by increasing temperature vs. latchretraction), all of them have one common feature. The stents areconnected with a wire extending outside the patient at all times andwhen they have to be removed, they are simply retracted back into thecatheter with or without prior softening of the material. For thisreason these stents cannot be left in the human body for more than acouple of days. The connecting wire can traverse the entire body if thestent is placed in the coronary or carotid artery from the femoralapproach, increasing risk of thrombus formation around the wire anddistal embolization, thrombosis of the femoral artery and infection ofthe inquinal region.

[0033] U.S. Pat. No. 5,941,895 to Myler et al. discloses a removablecardiovascular stent with engagement hooks extending perpendicular tothe axis of the stent into the vessel lumen. The stent retrievaltechnique requires introduction of an extraction catheter, which isadapted to grasp the engagement hooks of the stent with subsequent stentelongation in axial direction and reduction of its cross-sectionaldiameter. However, the stent with inwardly extending engagement memberswill likely require a larger delivery system than regular tubulardevices. Any manipulation of the catheters and guidewires in the stentedarea may potentially accidentally engage the hooks of the stent with itssubsequent dislodgment and damage of, the vessel. The hooks extendinginto the vessel lumen will cause turbulence of blood flow around them,leading to activation of the coagulation system and thrombus formation.

[0034] U.S. Pat. No. 5,833,707 to McIntyre et al. discloses a stentformed from a thin sheet of metal that has been wound around itself intoa general cylindrical tight roll and expands inside the body by heatingto body temperature. This stent is designed for predominant use in thehuman urethra and is not suitable for cardiovascular applications due tovery large metal surface that could be thrombogenic and increased sizeof the delivery system. The stent can be removed from the body with thehelp of a cannula or pincer grips for grasping the edge of the stent. Byrotating the pinched stent, the pincer or cannula cause the stent totelescopically coil into smaller diameter, which can then be retrievedfrom the urethra. This technique could be too traumatic forcardiovascular applications. The recovery apparatus will likely have alarge profile, making this method not practical or feasible forpercutaneous use in blood vessels or other tubular organs.

[0035] U.S. Pat. No. 5,562,641 to Flomenblit et al. discloses a spiralor cylindrical stent made from alloy with two-way shape memorycapabilities. The stent expands inside the body by heating to thetemperature of 50° C. to 80° C. with an electric current, injection ofhot fluid, external radio frequency irradiation or use of radiofrequency antenna inside the catheter. The stent can be removed from thebody after cooling to a temperature, ranging from −10° C. to +20° C., atwhich the stent partially collapses in diameter and can be grasped witha catheter for retrieval. As discussed above, heating of the stent to atemperature over 80° C. could be unsafe, especially with intravascularinjection of hot fluid. Use of external radio frequency irradiation willcause heating not only of the stent, but all tissues from the skinsurface to the stented vessel deep inside the body and beyond. Coolingthe stent to below the freezing temperature by injection of a very coldfluid into a blood circulation for removal is also impractical and notfeasible in a real clinical setting.

SUMMARY OF THE INVENTION

[0036] Accordingly, it is an object of the present invention to providenew and improved methods for delivering stents to desired locations inblood vessels and other tubular body structures.

[0037] Another object of the present invention is to provide new andimproved methods for delivering self-expanding stents to desiredlocations in body vessels by which the stent can be deployed in acontrolled gradual manner to thereby enhance the accuracy ofpositioning.

[0038] Still another object of the present invention is to provide newand improved methods for delivering self-expanding stents to desiredlocations in body vessels by which the stent can be deployed in acontrolled gradual manner safely without infusing a cooling liquid intothe vessel or otherwise affecting general body temperature or causingsystemic affects.

[0039] Yet another object of the present invention is to provide new andimproved methods for delivering self-expanding stents to desiredlocations in body vessels which eliminate the possibility of migrationof the stent during deployment.

[0040] A further object of the present invention is to provide new andimproved methods for repositioning and/or retrieving self-expandingstents in and from a body vessel without infusing a cooling or heatingliquid into the vessel or otherwise affecting general body temperatureor causing systemic affects.

[0041] A still further object of the present invention is to provide newand improved methods for repositioning and/or retrieving self-expandingstents which eliminates the possibility of migration of the stent duringrepositioning.

[0042] A still further object of the present invention is to provide newand improved methods for providing supplemental balloon angioplastyafter stent deployment with the same system, eliminating the need forexchanging catheters.

[0043] Briefly, in accordance with one aspect of the present invention,these and other objects are attained by providing a method fordelivering a self-expanding stent formed of a shape memory alloy to adesired location in a body vessel by placing the stent in a collapsedcondition in contact, or in other local heat transfer relationship, witha thermal transfer device coupled to a catheter assembly, and deliveringthe stent in its collapsed condition to the region of the desiredlocation in the body vessel while in contact or other local heattransfer relationship with the thermal transfer device. According to theinvention, the temperature of the thermal transfer device can becontrolled in a safe and non-invasive matter so that the expansion ofthe stent can be controlled (thereby enabling the precise positioning ofthe stent) by suitably varying the temperature of the thermal transferelement, and therefore the stent, during delivery and/or deployment.

[0044] For example, in the case where the stent is made of a shapememory alloy having a transition temperature such that the stent fromwhich it is formed is in its expanded diameter state at or slightlybelow body temperature (37° C. ), the temperature of the thermaltransfer device is maintained below body temperature during delivery ofthe stent and at the beginning of deployment to allow precisepositioning, while in the case where the stent is made of a shape memoryalloy having a transition temperature such that the stent obtains itsexpanded diameter state at a temperature greater than body temperature,the temperature of the thermal transfer element is increased to thehigher temperature after the stent in its collapsed state has beenprecisely positioned at the desired location whereupon the stent expandsto its expanded diameter state.

[0045] The thermal transfer device is constructed such that thetemperature of the stent can be controlled quickly, precisely andnon-invasively. Specifically, the temperature of the stent can bechanged quickly since the stent is in local heat transfer relationshipwith the thermal transfer device. For present purposes, “local heattransfer relationship” means either the stent contacts the thermaldevice or the stent and thermal transfer device are sufficiently close,so that heat is transferred between the stent and the thermal transferdevice without materially affecting the temperature of the surroundingtissue. The stent's temperature can be controlled relatively preciselysince the temperature of the stent, which has a low mass, willessentially correspond to the temperature of the thermal transferdevice, which has a much higher mass. Moreover, no liquid or gas will beinfused into the vessel during the entire procedure, such as in the caseof Harada et al U.S. pat. No. 5,037,427.

[0046] In preferred embodiments of the invention, the thermal transferdevice comprises an arrangement itself capable of controlled radialexpansion to about the diameter of a stent in its expanded diameterstate, and contraction to a collapsed state. This feature, in some ofits embodiments, is not only advantageous with respect to the initialdelivery of a self-expanding stent with an option of performing aballoon angioplasty at the same time, but, additionally, makes thearrangement particularly adapted for repositioning and/or retrievingstents formed of two-way shape memory alloys that have already beendeployed in a vessel, such as in the repositioning of a misplaced stent,removal of a stent placed for temporary indications, or the removal of astent that has completed the delivery of mediation or radiation to aparticular area. Specifically, for removal and/or repositioning of thestent, the thermal transfer device is structured and arranged to beinitially positioned in the lumen of the already deployed stent in acollapsed condition, out of contact or other local heat transferrelationship with the deployed stent, and then expanded into contact, orother local heat transfer relationship with the stent. The temperatureof the heat transfer device is adjusted so that the temperature of thedeployed stent is reduced to that at which the stent obtains a relaxed,flexible state whereupon it separates from the vessel wall. The stentcan then be drawn into the catheter assembly and either removed from thebody or repositioned using the initial delivery process described above.

[0047] In one embodiment of the method, the thermal transfer devicecomprises an inflatable and expandable balloon member, and the initialdelivery of a stent formed of a shape memory alloy can be assisted inthe manner of angioplasty by inflating the balloon to forcibly urge thestent against the vessel walls.

[0048] In accordance with another aspect of the invention, the catheterassembly includes a capturing device for releasably coupling the stentto the catheter assembly during deployment, as well as for grasping analready-deployed stent for purposes of retrieval and/or repositioning.The capturing device prevents the stent from being carried away by thebloodstream or from migrating on the catheter, and is also structuredand arranged to assist in drawing the stent in its flexible and pliablecondition into the catheter assembly for repositioning and retrieval.

[0049] In a preferred embodiment, the thermal transfer device comprisesa balloon member connected to a catheter assembly defining a containedchamber having an outer wall, at least a part of which constitutes athermal transfer material. The arrangement further includes apparatusfor circulating a thermal transfer fluid from the proximal end region ofthe catheter assembly into the interior of the chamber and for providingan outflow of the thermal transfer fluid from the interior of the closedchamber to the proximal end region of the catheter assembly. As usedherein, the term “fluid” refers to either a liquid or a gas. Thetemperature of the circulating thermal transfer fluid is controlledeither by heating or cooling means situated at the proximal end of thecatheter assembly outside of the body, or by heating means situatedwithin the chamber of the thermal transfer device, such as optic fibersfor transmitting a laser beam to heat the fluid circulating within thethermal transfer device, an internal ultrasound probe situated withinthe thermal transfer device, or a spiral resistance heating wire whichwill be heated by induction of an electric current by applying the powersource or magnetic field from an external source. Alternatively, thesurface of the balloon can be heated for direct heat transfer to thestent. For example, resistance heating wires may be situated on theouter surface of an expandable balloon, as can a spiral surface wirewhich can be heated by induction through the application of a powersource or magnetic field from an external source, or externally situatedoptic fibers for transmitting a laser beam along and around the surfaceof the balloon. The stent is in contact with the heat transfer surfaceduring delivery and depending on the transition temperature of the alloyfrom which the stent is made, the stent is either cooled, heated, orleft at ambient temperature through contact or other local heat transferrelationship during delivery. In capturing an already deployed stent,the balloon in its collapsed condition is situated in the lumen of thealready deployed stent, and then expanded into contact with the stent.Cooling liquid is circulated through the balloon which cools the stentcausing it to separate from the vessel wall and to become flexible andpliable so that it can be drawn into the catheter assembly.

[0050] In another preferred embodiment, the thermal transfer devicecomprises an expandable frame formed from a plurality of conductiveresistance wires. The frame can be expanded by suitable adjustment ofthe catheter assembly to bow the resistance wires radially outwardlyinto contact with the stent. The wires are heated by connection to anexternal source of electricity and are in direct contact heat transferrelationship with the stent.

DESCRIPTION OF THE DRAWINGS

[0051] A more complete appreciation of the present invention and many ofthe attendant advantages thereof will be readily understood by referenceto the following detailed description when considered in connection withthe accompanying drawings in which:

[0052]FIG. 1 is a perspective view of a first embodiment of a catheterassembly, including a first version of a hook-type stent capturingdevice, and an associated sleeve-type thermal transfer device for use inaccordance with the invention, with the thermal transfer device shown inexpanded condition;

[0053]FIG. 2 is a perspective view of the first embodiment with thethermal transfer device in a collapsed condition;

[0054]FIG. 3 is a perspective view of the first embodiment, partiallybroken away to show the hook-type stent capturing device of the catheterassembly for use in accordance with the invention;

[0055]FIG. 4 is a perspective view of a first version of a secondembodiment of a catheter assembly and associated “solid” thermaltransfer device in an expanded condition for use in accordance with theinvention, with a first version of an arrangement for circulatingthermal transfer fluid through the thermal transfer device, and ahook-type stent capturing device;

[0056]FIG. 5 is a perspective view of a first version of the secondembodiment, partially broken away to show the first version of thecirculation arrangement;

[0057]FIG. 5a is a section view taken along line A-A of FIG. 5;

[0058]FIG. 5b is a section view taken along line B-B of FIG. 5;

[0059]FIG. 6 is a transverse section view of the embodiment of FIG. 5through the stent-receiving sheath;

[0060]FIG. 7 is a perspective view of the second embodiment with thethermal transfer device in a collapsed condition;

[0061]FIG. 8 is a perspective view of a second version of the secondembodiment, with a second version of the thermal transfer fluidcirculating arrangement;

[0062]FIG. 8a is perspective view of another version of the secondembodiment, with a second version of a stent-capturing device;

[0063]FIG. 8b is a perspective view of still another version of thesecond embodiment, with a third version of a stent-capturing device;

[0064]FIG. 8c is a perspective view of yet another version of the secondembodiment which does not utilize a frame assembly;

[0065]FIG. 9 is a perspective view of the second version of the secondembodiment, partially broken away to show the second version of thecirculation arrangement;

[0066]FIG. 9a is a section view taken along line A-A of FIG. 9;

[0067]FIG. 9b is a section view taken along line B-B of FIG. 9;

[0068]FIG. 9c is a perspective view of a modification of the secondversion of the second embodiment, but partially broken away to show themodification of the second version of the circulation arrangement;

[0069]FIG. 9d is a section view taken along line D-D of FIG. 9c;

[0070]FIG. 9e is a section view taken along line E-E of FIG. 9c;

[0071]FIG. 10 is a perspective view of the second version of the secondembodiment, with the thermal transfer device shown in a collapsedcondition;

[0072] FIGS. 11 (a)-11 (g) are seven perspective views showingsequential steps of operation of the first and second versions of thesecond embodiment of the invention in connection with the deployment ofthe stent;

[0073]FIG. 11h shows two partial perspective views showing the sequenceof withdrawal of the stent-receiving sheath from the conus;

[0074] FIGS. 12(a)-12( 1 ) are twelve perspective views showingsequential steps of operation of the first and second versions of thesecond embodiment of the invention in connection with repositioningand/or retrieving an already positioned stent;

[0075]FIG. 13 is a perspective view of a first version of a thirdembodiment of a catheter assembly, including another version of a stentcapturing device, and associated sectored thermal transfer device in itsexpanded position for use in accordance with the invention, with thefirst version of a thermal transfer fluid circulation arrangement;

[0076]FIG. 14 is a perspective view of the first version of the thirdembodiment, partially broken away to show the first version of thecirculation arrangement;

[0077]FIG. 14a is a section view taken along line A-A- FIG. 14;

[0078]FIG. 14b is a section view taken along line B-B of FIG. 14;

[0079]FIG. 15 is a longitudinal sectional view of the first version ofthe third embodiment;

[0080]FIGS. 16a-c are three perspective views showing sequential stepsof the collapse of the first version of the third embodiment of thethermal transfer device from its expanded diameter condition;

[0081]FIG. 17 is a perspective view of the second version of the thirdembodiment of the invention, with the second version of the thermaltransfer fluid circulation arrangement;

[0082]FIG. 18 is a perspective view of the second version of the thirdembodiment, partially broken away to show the second version of thecirculation arrangement.

[0083]FIG. 18a is a section view taken along line A-A of FIG. 18;

[0084]FIG. 18b is a section view taken along line B-B of FIG. 18;

[0085]FIG. 19 is a longitudinal section view of the second version ofthe third embodiment;

[0086]FIGS. 20a-20 c are three perspective views showing sequentialsteps of the collapse of the second version of the third embodiment ofthe thermal transfer device from its expanded diameter condition;

[0087]FIG. 20d is a perspective view of a modification of the secondversion of the third embodiment, partially broken away to show themodification of the second version of the circulation arrangement;

[0088]FIGS. 20e and 20 f are section views of a modification of thesecond version of the third embodiment taken along lines E-E and F-Frespectively in FIG. 20d;

[0089]FIGS. 21a-21 f are six perspective views showing sequential stepsof the operation of the second version of the third embodiment of theinvention in connection with deploying a stent, and also illustratingthe corresponding operation of the catheter assembly at its proximalend;

[0090]FIGS. 22a-22 g are seven perspective views showing sequentialsteps of the operation of the second version of the third embodiment ofthe invention in connection with retrieving the stent, and alsoillustrating the corresponding operation of the catheter assembly at itsproximal end;

[0091]FIG. 23 is a perspective view of the first embodiment for use inthe invention with the thermal transfer device in a collapsed conditionand including a snare-type stent capturing device;

[0092]FIG. 24a is an elevation view of the entire third embodiment ofthe catheter assembly and associated sectored thermal transfer device;

[0093]FIG. 24b is a perspective view of the third embodiment of theinvention with a stent pre-mounted on the collapsed thermal transferdevice;

[0094]FIG. 25 is a perspective view of the proximal end of the catheterassembly of the first version of the third embodiment of the invention;

[0095]FIG. 26 is a perspective view of the proximal end of the catheterassembly of the second version of the third embodiment of the invention;

[0096]FIG. 27 is a perspective view of a fourth embodiment of thecatheter assembly and associated thermal transfer device for use inaccordance with the invention;

[0097]FIG. 28 is a perspective view of a fifth embodiment of a catheterassembly and associated thermal transfer device for use in accordancewith the invention;

[0098]FIG. 29 is a perspective view of a sixth embodiment of a catheterassembly and associated thermal transfer device for use in accordancewith the invention;

[0099]FIG. 30 is a perspective view of a seventh embodiment of acatheter assembly and associated thermal transfer device for use inaccordance with the invention;

[0100]FIG. 31 is a perspective view of an eighth embodiment of acatheter assembly and associated thermal transfer device for use inaccordance with the invention; and

[0101]FIG. 32 is a perspective view of a ninth embodiment of a catheterassembly and associated thermal transfer device for use in accordancewith the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0102] Various embodiments of apparatus for delivering a self-expandingstent and/or for retrieving and repositioning an already-positionedself-expanding stent in accordance with the invention are describedherein. In all cases, where the apparatus is to be used for delivering astent, the stent may be formed of a shape memory material having eithera one-way shape memory or a two-way shape memory. However, in the casewhere the apparatus is to be used for retrieving and/or repositioning astent that is already in place, the stent must be formed of a two-wayshape memory alloy.

[0103] For purposes of describing the invention, except where noted, thestent to be delivered, retrieved and/or repositioned is formed of atwo-way shape memory material having or trained to have a second coldmemory. When released into the vessel or other tubular structure andnaturally warmed to first transition temperature at or below bodytemperature of 37° C. , the stent expands and recovers its previouslyimprinted intended functional shape at or below body temperature. In afully expanded state within the human body, the stent is capable ofexerting considerable radial force on the surrounding structures, whichallows mechanical opening of the vessel lumen and maintaining itslong-term patency for free passage of flow. When the fully expandedstent is cooled to a temperature in the range of −10° C. to +35° C. , itbecomes compliant, has a reduced stress state, and can be compressedinto a reduced diameter, small enough to fit within a low profiledelivery system for percutaneous insertion.

[0104] The stent is constructed of a single continuous thermal shapememory wire, can be cut with laser technology, or formed with aphotoetching technique from thermal shape memory tubing to create amesh-like configuration. The expansive force and the stiffness along thelength of the stent can be modulated by changes in the dimensions of thecell geometry. There are no open or sharp edges at either end of thedevice. This prevents injury to the wall while improving the ability toposition, reposition or retrieve the device. Because the wire neveroverlaps itself, the stent wall thickness is never greater than the wirediameter and both surfaces are smooth. The cells of the stent create anopen mesh, which is favorable for maintaining the patency of sidebranches, and also minimized the length changes, which occur between thecollapsed and expanded forms of the device. The shortening of the stentduring its expansion depends on the cell geometry, but usually does notexceed 10% of the length of the stent in its completely expanded state.In a preferred embodiment, an intraluminal medical device may include apermanent or temporary implantable stent or stent-graft, a permanent ortemporary device impregnated with medications or radioactivity for localtherapy, or a temporary retrievable/repositionable device.

[0105] For the purpose of non-surgical treatment of vascular aneurysms,acutely bleeding vessels, or other perforated tubular organs (GI tract,bile ducts, tracheo-bronchial tree etc.), the stent can be covered witha graft material or coating. The graft material is anchored at each endto an exposed section of the metallic scaffold of the stent. The designof the device is such that length changes that occur during delivery canbe largely limited to the short uncovered stent segments at either endof the device. The stents can also be impregnated with certainmedications or provided with a radioactive coating, for local deliveryof drugs or radiation to the diseased vessel.

[0106] Referring now to the drawings in which like reference charactersdesignate identical or corresponding parts throughout the several views,and more particularly to FIGS. 1-3, a first embodiment of apparatus inaccordance with the invention comprises a catheter assembly 50A (onlythe distal end region of which is shown), a thermal transfer device 60Aconnected to catheter assembly 50A and an associated stent capturingdevice 70A. Catheter assembly 50A comprises a low profile outer corecatheter 8, having an inner movable core catheter 3, an innerstent-capturing sheath 19 situated over the outer core catheter 8, andan outer stent-receiving sheath 11. In this embodiment, the thermaltransfer device 60A comprises a frame assembly 62 to which an expandableballoon 4 is connected. Balloon 4 has a sleeve-type configuration, i.e.,the balloon 4 has an annular cross-section along its entire length. Asdiscussed below, this shape is advantageous since the flow of blood orother body fluid which normally occurs in the vessel will be maintainedduring inflation of the balloon through the opening 16 in the center ofthe balloon 4. As described below, the balloon is formed of materialhaving suitable thermal transfer characteristics, i.e. relatively goodheat conductivity. The frame assembly 62 includes a plurality ofscaffolding wires 5, each wire 5 having a distal end molded into a conus2, which has a tapered configuration for easy percutaneous insertion,and a proximal end 9 molded into the outer core catheter 8. Thescaffolding wires are preferably formed of a material that exhibitssuperelastic properties.

[0107] The outer core catheter 8 has a distal end which is situatedproximally to the distal end of the inner core catheter 3 so that aprojecting portion of the inner core catheter 3 extends beyond thedistal end of the outer core catheter 8. Each of the scaffolding wireshas one end fixed to the distal end of the projecting portion of theinner core catheter 3 at conus 2, another end fixed to the distal end ofthe outer core catheter 8, and a central region attached to the balloon4.

[0108] It will be seen that by relative movement of the inner and outercore catheters to shorten the projecting portion of the inner core, thewires 5 will bow or bend and therefore expand the balloon to itsexpanded condition shown in FIG. 1. On the other hand, relative movementof the inner and outer core catheters to lengthen the projecting portionof the inner core straightens the wires and collapses the balloon to itscollapsed condition as seen in FIG. 2. The frame assembly can be formedin other manners, such as by the use of elongate plastic memberssimilarly affixed to the inner and outer core catheters.

[0109] The sleeve-type balloon 4 is formed of a thin elastic sheetmaterial of the type used for conventional balloon angioplastycatheters, such as polyethylene or other polymer film for example,having a thickness of about .001 inches, or other thin flexiblebiocompatible material having thermal transfer properties, sufficientfor the present purpose. In expanded condition the balloon has an outercylindrical wall 4 a, an inner cylindrical wall 4 b, and top and bottomwalls 4 c and 4 d, together defining an interior chamber. The centralregions of each of the six scaffolding wires 5 pass through narrowpassages 5 a formed in the outer surface of the outer wall 4 a ofballoon 4, to couple the frame assembly 62 to the balloon 4 as seen inFIG. 1 and as noted above, the frame 5 can be stretched and collapsed byadvancing the movable inner core 3 forward while the outer core catheter8 is fixed thereby radially collapsing balloon 4.

[0110] The inner core catheter 3 has inflow and outflow fluid channels,formed in its wall extending from the proximal end of the catheterassembly to the distal end thereof. Inflow and outflow channels arefluidly connected at their distal ends to the interior chamber ofballoon 4 by connecting inflow and outflow tubes 7 and 6 respectively. Apump or an infusion apparatus (not shown) is situated at the proximalend of the catheter assembly for circulating a thermal transfer fluid,such as a cold or hot saline liquid or gas (i.e. a fluid at atemperature sufficient to achieve the transition temperature of thestent), into the chamber of balloon 4 through inflow fluid channel andinflow tube 7 to fill the chamber, and then out from the balloon chamberthrough outflow tube 6 and outflow fluid channel. The term “fluid” isused herein in its broad sense and comprises both liquids and gases.

[0111] Alternatively, the inflow channel can be connected to apressurized canister filled with a gas or liquid, hereinafter referredto as a “thermal fluid”, at a suitable temperature. Thermal fluid canalso be injected by a syringe or by means of a pressure bag. Thermalfluid fills the balloon chamber and before this liquid or gas warms upinside the balloon, escapes into the outflow channel through outflowtube 6 and then to outside the patient at the other end of the system,where it may be collected in a bag (see FIG. 24a). This allowspersistent local maintenance of a desired temperature of the outer wall4 a of balloon 4 which constitutes a thermal transfer wall of thethermal transfer device .

[0112] As seen in FIGS. 1-3, the stent-capturing device 70A comprises aplurality of resilient stent-capturing hooks 17 having hook portions 17a and shank portions 17 b, molded into the wall of the stent capturingsheath 19 moveably situated over the outer core catheter 8. The hookportions 17A are normally spring biased outwardly to the positions shownin FIG. 1. The resilient portions of the hooks 17 can be at leastpartially covered with a thin membrane 95 to facilitate safe andaccurate capturing and holding of the stents as described below. Thestent-receiving sheath 11 in its retracted position as seen in FIGS. 1and 2 has a flared end region 10. The hooks 17 can be opened or closed,i.e., the hook portions 17 a moved radially outwardly or inwardly duringdeployment, retrieval or repositioning of an already deployed stent byadvancing or withdrawing, respectively, the stent-receiving sheath 11whereby the hook portions 17 a are controllably engaged by the flaredend region 10.

[0113] As seen in FIGS. 11b and 11 h, when the catheter assembly isintroduced into the body, the end region of the stent-receiving sheathis in a closed condition in sealing engagement within a groove 2 aformed in the conus 2. When the stent-receiving sheath is withdrawn toexpose a preloaded stent or balloon, the tip assumes its flaredconfiguration for facilitating the reception and subsequent removal ofthe collapsed stent (FIG. 11h).

[0114] As described below in connection with FIGS. 11 and 12, the systemis introduced into the body with the frame assembly 62 and balloon 4 ofthermal transfer device 60A in their collapsed condition and covered bythe stent-receiving sheath 11. As seen in FIGS. 1-3 the inner corecatheter 3 has a central lumen for receiving a guidewire 1 and tworadiopaque markers 15 are provided on the moveable inner core catheterfor precise positioning and operation under fluoroscopic guidance.

[0115] A first version of a second embodiment of the invention isillustrated in FIGS. 4-7. This embodiment is similar to the embodimentof FIGS. 1-3 in that it includes a catheter assembly 50B, a thermaltransfer device 60B and a stent-capturing device 70B operationallyconnected thereto. The second embodiment differs from the firstembodiment mainly in that the thermal transfer device 60B comprises asolid-type balloon 12 rather than the sleeve-type balloon 4 of the firstembodiment. In other words, while a transverse cross-section of thesleeve-type balloon 4 is an annulus, the solid balloon has a circulardisk-shaped transverse cross-section. The distal end of balloon 12 issealingly connected to the introducing conus 2 or to the distal end ofthe inner core catheter 3, while the proximal end of balloon 12 issealed to the more proximal aspect of the inner core catheter at 18thereby defining a chamber. The balloon 12 is made of the same type ofmaterial as in the case of the first embodiment. The central region 12 aof the balloon constitutes a thermal transfer wall as discussed below.Like the first embodiment, the thermal transfer device also includes aframe assembly 62A comprising a plurality of scaffolding wires 5, thedistal ends of which are molded in the conus 2 fixed to the distal endof the inner core catheter 3, the proximal ends of which are molded tothe outer core catheter 8, and central regions of which extend throughpassages 5 a formed in the outer surface of the balloon 12.

[0116] The second embodiment of the invention shown in FIGS. 4-7 alsoincorporates apparatus for circulating a thermal transfer fluid into andfrom the interior chamber of balloon 12. While the inner moveable core 3has a central lumen for the guidewire 1 in the same manner as in thefirst embodiment, two continuous channels 13 and 14 are provided in theinner core 3. Channels 13 and 14 extend from the proximal end of theinner core catheter 3 and open at respective ports 13 a and 14 asituated within the chamber of balloon 12. Channel 14 is used forinfusion of a thermal fluid into the chamber of balloon 12 while channel13 is used as an outflow channel. By suitably connecting the proximalend of channel 14 to a pump, or other source of infusion of thermalfluid, and by suitably connecting the proximal end of channel 13 to acollecting container, a constant circulation of the thermal transferfluid through the balloon 12 is achieved. Alternatively, the thermalfluid can recirculate through a closed circuit pump system. Inflowchannel 14 and outflow channel 13 can be interchanged so that channel 14is used for outflow while channel 13 is used for inflow.

[0117] Referring to FIG. 7, as described below in connection with FIGS.11 and 12, the thermal transfer device 60B can be collapsed in the samemanner as thermal transfer device 60A by advancing the moveable corecatheter 3 forwardly while holding the outer core 8 fixed.Alternatively, the thermal transfer device 60B can be collapsed byfixing the inner core catheter 3 in place and withdrawing the outer corecatheter 8. The stent-capturing device 70B essentially corresponds tothe stent-capturing device 70A.

[0118] A second version of the second (solid balloon) embodiment isillustrated in FIGS. 8, 9 and 10. This version essentially differs fromthe first version of the second embodiment in the construction of thethermal transfer fluid circulation system. The proximal end of balloon12 is sealingly attached to the outer core catheter 8 at 18 a and thespace between the outer core catheter 8 and the inner movable corecatheter 3 functions as an inflow channel for thermal fluid 25 whichopens into the chamber defined by balloon 12. An outflow channel 13 isformed in inner core catheter 3 which terminates at a port 13 acommunicating with the balloon chamber. In this manner, one of the twochannels in the inner core catheter 3 required in the first version ofthe second embodiment can be eliminated.

[0119] A modification of the second version of the second embodiment isshown in FIG. 8a, where the frame wires 5 are paired and interconnectedwith a single bridging bar 98 in their central portions. Thestent-capturing sheath 19 with the capturing hooks are eliminated inthis modification. Instead, there are at least four capturing wires 96,which are molded to the inner core catheter 3 at the base of conus 2.The capturing wires 96 extend parallel to the frame wires 5, but outsidethe balloon 12 and pass under the bridging bars 98 between the centralportions of the paired frame wires 5. The relative motion of the movablecore 3 and the outer core catheter 8 promotes opening and closing of thecapturing wires 96. When the balloon 12 is expanded, capturing wires 96open with it. When the balloon is slowly deflated, the capturing wires96 stay open and do not follow the collapsing balloon until the angledportion of the capturing wires become engaged with the bridging bars 98,which will facilitate closing of the capturing wires over the balloon.

[0120]FIG. 8b demonstrates another modification of the second version ofthe second embodiment. The balloon and frame are similar to the secondversion of the second embodiment, but the stent-capturing mechanismconsists of four capturing wires 96 which are molded to the inner corecatheter at the base of the conus 2. The capturing wires 96 extendparallel to the frame wires 5, but outside the balloon 12 and passthrough the rings 97 attached to the central portions of the frame wires5. The mechanism of opening and closing of the capturing wires 96 issimilar to the one described in FIG. 8a with the only difference thatthe capturing wires 96 pass through the rings 97 on the frame instead ofextending under the bridging bars 98 between the parallel paired wiresin FIG. 8a.

[0121] Yet another modification of the second version of the secondembodiment is illustrated in FIG. 8c, where the solid type balloon doesnot have any metallic frame, but has an inflow channel 25 and an outflowchannel 13, and can be expanded and collapsed by relative motion of theinner movable core 3 along the outer core catheter 8 in conjunction withinjection of the thermal fluid under pressure.

[0122] Referring to FIGS. 9c-9 e, a modification of the second solidballoon embodiment of the invention is illustrated. In this embodiment,the thermal transfer device 60B comprises a balloon 12 having an outerwall 12 a and an inner wall 40 attached to the inner surface of theouter wall 12 a of the balloon at equally spaced locations, preferablyat the wire sleeves 5a receiving the frame wires 5, as best seen in FIG.9d. The inner wall 40 and outer wall 12 a of the balloon define an outerchamber 42 between them while the inner wall 40 defines an inner chamber44. The inflow of a thermal fluid into the outer chamber 42 is providedthrough channel 32. There are multiple perforations in the inner wall 40of the balloon, and the thermal fluid escapes into the inner chamber 44of the balloon after being transiently trapped between the inner andouter layers of the balloon for more efficient thermal transfer throughthe outer balloon wall 12 a. The thermal fluid then escapes into thespace between the outer core catheter 8 and the movable core catheter 33and is collected into an attached bag at the proximal end of thecatheter assembly outside the patient. All other components of thesystem and mechanisms of its delivery/retrieval and operation remain thesame as described above in the embodiments of FIGS. 4, 5, 6 and 7.

[0123] The systems comprising the sleeve type balloon (FIGS. 1-3) andthe solid type balloons (FIGS. 4-10), provided with the stent-capturinghooks 17, are beneficial for primary delivery, repositioning or removalof stents including stent-graft devices or covered/coated stents.

[0124] Referring to FIG. 11, a clinical scenario of primary stentdelivery and deployment into a focal narrowing 80 a of a vessel 80 isshown in stages. The stent is formed in accordance with the method ofthe invention of either a one-way or two-way shape memory alloy having afirst transition temperature at or below the body temperature. Inutilizing the apparatus described above for primary stent delivery, astent is initially mounted on the thermal transfer device in itscollapsed condition and so that the stent is in thermal transferrelationship with the collapsed thermal transfer device. Preferably, thesystem is provided to the operator in a closed configuration (seen inFIG. 11b) in which the stent-receiving sheath 11 is in a forwardposition covering the collapsed stent 90, which has already beenpreloaded or mounted (such as by crimping) in contacting engagement overthe collapsed balloon 12 and with the stent capturing hooks 17 securedto it. In the closed configuration, the distal end 11 a of thestent-receiving sheath 11 is received in a groove 2 a of conus 2 to sealthe space within sheath 11 from the entry of blood or other body fluidsin vessel 80 during delivery.

[0125] The system is introduced into the vessel and positioned underdirect fluoroscopic guidance (with the assistance of positioning markers15) such that the position 11 b of the delivery system with thepremounted stent 90 is situated in the area of narrowing 80 a of vessel80 (FIG. 11b). During this delivery, the stent-receiving sheath 11 atleast partially thermally insulates the collapsed stent 90 from bodyheat thereby maintaining the temperature of the stent 90 below bodytemperature.

[0126] Referring to FIG. 11c, deployment of stent 90 begins when theoperator retracts or withdraws the stent-receiving sheath 11 exposingthe collapsed stent 90 mounted on the collapsed balloon 12 to the vesselinterior and to body heat (see FIG. 24b). The circulation of a coldliquid or gas through the chamber of balloon 12 is started at about thesame time as the sheath 11 is withdrawn. For example a cool salinesolution is infused from the proximal end of the catheter assembly 50Athrough inflow channel 14 into the balloon chamber through port 14 a andrecirculates back through port 13 a and outflow channel 13. Thetemperature of the stent 90 is thereby maintained below the transitiontemperature preventing premature expansion of the stent by the localtransfer of thermal energy through the wall of the balloon 12 into thethermal transfer fluid. The balloon 12 remains in its collapsed positionat this time by maintaining the outflow channel 13 open. A precisepositioning of stent 90 is enabled by controlling the expansion of stent90 through the circulation of cooling thermal fluid even after thesheath 11 is retracted and the stent is exposed to body temperature.When the operator is satisfied that the stent 90 is precisely positionedin the desired location 80 a of the focal narrowing of vessel 80, thestent-capturing hooks 17 are opened and disconnected from stent 90 byfurther withdrawing of the stent-receiving sheath 11 with respect to thestent-capturing sheath 19, and the infusion of the cooling thermal fluidis stopped. The opened hooks are withdrawn toward the stent- receivingsheath before the stent expands to avoid interference with the stent asit expands. The stent 90 then warms naturally to body temperaturethrough contact with surrounding blood or other body fluids or gas, andexpands towards its original predetermined shape (FIG. 1d). The stent isthus deployed into supporting engagement with the wall of vessel 80 andexerts an outward force against the wall to open the focal narrowing 80a of vessel 80.

[0127] Balloon angioplasty of the deployed stent can then be performedif clinically indicated. This can be achieved by closing the outflowchannel 13 with a provided stop-cock. The balloon is expanded byexpansion of the frame assembly 62 and infusion of a contrast materialdiluted in normal saline through the infusion port 14 a, which allowsvisualization of the balloon under real time radiological control (FIG.11e). Opening the frame assembly 62 is achieved by moving the outer corecatheter 8 forward relative to inner core catheter 3 which helpsexpansion of the balloon 12. High pressure can be achieved inside theballoon 12, which is regulated and controlled by a pressure manometerconnected to the inflow channel outside the patient. Angioplasty (FIG.11e) can be performed sequentially several times if so desiredclinically.

[0128] The balloon 12 is then deflated by opening the outflow channel 13and the frame assembly 62 collapsed by moving the outer catheter 8 back(FIG. 11f). The collapsed balloon is then withdrawn back into thestent-receiving sheath 11 whereupon the system can be removed from thebody, leaving the stent in place (FIG.11g). As noted above, this systemcan be used for deployment of stents exhibiting one-way or two-waymemory.

[0129] The same system can be used for delivery and precise positioningof stents which are formed of shape-memory alloys that have a transitiontemperature greater than body temperature and which therefore expand totheir predetermined configurations at temperatures higher than bodytemperature. Such a stent is delivered in the area of interest in thecollapsed state covered with the outer sheath 11 and then exposed bymoving the sheath 11 backwards. No infusion of cold thermal transferfluid is needed to keep the stent in its collapsed state since thetemperature of the stent will only rise to body temperature which isbelow the transition temperature. The stent therefore remains mounted onthe collapsed balloon 12 secured to the catheter assembly bystent-capturing hooks. When the position of the device is adjusted andthe desired location of the stent is confirmed, the stent-capturinghooks 17 are opened by further withdrawing of the stent-receiving sheath11, releasing the stent 90 and the infusion of a warm solution at leastat the transition temperature which is higher than body temperature isstarted through the inflow channel 14. The frame assembly 62 is openedby moving the outer core catheter 8 forward. These maneuvers allowexpansion of the mounted stent inside the area of stenosis providinghigh radial force on the walls of the vessel due to its heating to thetransformation or transition temperature. If clinically indicated aprimary stent placement can be supplemented with a balloon angioplastywith the help of the same delivery system. This can be achieved byclosing the outflow channel and infusion of a diluted contrast materialthrough the inflow channel in the manner described above.

[0130] Referring to FIG. 12, a clinical scenario is given when the stent90 has been malpositioned inside the vessel only partially covering thearea of stenosis (FIG. 12a) and it is desired to reposition the stent.In this case, the stent 90 is formed of a two-way shape memory alloy.For example, the alloy may have a first transition temperature equal toor below body temperature, and a second lower transition temperature inthe range of between −10° C. to +35° C. The system is introduced withthe balloon 12 in a collapsed state and covered with the stent-receivingouter sheath 11 (FIG. 12b) and positioned at the desired location suchthat the collapsed balloon 12 is situated within the lumen of stent 90that is intended to be retrieved or repositioned. The outer sheath 11 iswithdrawn, the distal end 11 a obtaining a flared configuration, therebyexposing the frame assembly 62A and the collapsed balloon 12 (FIG. 12c).The metallic frame assembly is opened and the outer core catheter 8advanced while the movable inner core catheter 3 is fixed in place (FIG.12d). Expansion of the frame assembly 62A brings the outer wall ofballoon 12 into close contact with the stent. At this time the infusionof a cold thermal fluid into the chamber of balloon 12 is startedthrough the inflow channel 14 and the balloon 12 is inflated withoutcreating high internal pressure within it due to an open outflow channel13. The diameter of the open wire frame 62A matches the internaldiameter of the stent and the cold balloon 12 moves into direct contactwith the stent, causing its local cooling to the temperature at or belowthe second transition temperature, e.g. in the range of −10° C. to 35°C., through the thermal transfer wall forming balloon 12. The stentbecomes soft and pliable at this temperature and reduces at leastsomewhat in diameter to separate from the wall of vessel 80. The nextstep includes slowly stretching the wire frame 62 to a smaller diameterby moving the outer core catheter 8 backwards and keeping the movablecore catheter 3 of the system in the same position. Start this maneuvercauses a slow collapse of the frame assembly (FIG. 12e). The infusion ofcold thermal transfer fluid continues, but the balloon 12 moves awayfrom the wall of the vessel 80 or other tubular structure due tostretching of the wire frame. The stent, or its proximal end in the casewhere the stent is designed to operate as such, begins to collapseinwardly “hugging” the outer wall of balloon 12 and the frame. At thistime the stent-capturing hooks 17 are maneuvered to close over thecollapsed proximal end of the stent by suitable manipulation of thestent-capturing sheath 19 (FIG. 12f). This causes secure fixation of thesoftened cooled stent to the catheter assembly. The stent is then drawninto the stent-receiving sheath 11 with a flared tip 11 a and infusionof the cold solution/gas into the balloon 12 is terminated (FIG. 12g).Collapse of the proximal end of the stent prevents migration of thedevice and slippage over the balloon due to persistent contact of thedistal two thirds of the stent with the vessel wall, even though theentire stent becomes very soft.

[0131] The stent can be then completely removed from the body orrepositioned while inside the stent-receiving sheath 11 into the properlocation (FIG. 12h). In this latter case, the stent is then unsheathed(FIG. 12i), warms to body temperature and then expands into the originalshape and diameter after the stent-capturing hooks are released (FIG.12j and FIG. 12k). The reposition and retrieval system is then removedfrom the body and the repositioned stent remains in place (FIG. 12l).Stent retrieval is beneficial in patients where the indication forprimary stent placement is an acute intimal dissection, where the stentsare used as the vehicle for local delivery of medications or radioactivesubstances, or in the situations when repositioning of misplaced stentis required.

[0132] The same system can be used for retrieval or repositioning of astent made from two-way shape memory alloy having a first transitiontemperature greater than body temperature and therefore a stentexpanding to its original shape at higher than body temperature. Thesestents require cooling to a temperature below 37° C. in order to exhibitsecond way memory and partially collapse for safe retrieval, with allother steps similar to the ones described in connection with FIG. 12. Ifrepositioning of such a stent is required after it has been recoveredinto the outer sheath, the position of the closed system is adjustedunder direct fluoroscopic guidance. The mounted captured stent isunsheathed and stays in the collapsed state without infusion of a coldsolution since the first transition temperature is greater than bodytemperature. After the stent is precisely positioned at the desiredlocation, the stent-capturing hooks are opened by completely withdrawingthe stent-receiving sheath 11 , releasing the stent. A warm solution isinfused into the balloon chamber through the infusion port 14 a and themetallic frame 62 is opened by moving the outer core catheter forwardalong the fixed movable core. The steps of repositioning of such a stentare the same as for the primary delivery of the stent with thetemperature of transformation, i.e. the transition temperature, higherthan body temperature, which is described above and can be supplementedwith an angioplasty in the same fashion if so desired clinically.

[0133] Referring to FIGS. 13-16, a first version of a third embodimentof apparatus in accordance with the invention comprises a thermaltransfer device 60C associated with a catheter assembly 50C andincluding a stent capturing device 70C. The thermal transfer device 60Ccomprises an inflatable and collapsible balloon 20 formed of the sametype of material as that from which balloons 4 and 12 are made. Theballoon 20 has a cloverleaf configuration in the cross sectional view(FIG.14a). Balloon sectors 20 ₁-20 ₄ merge with each other at theproximal and distal ends of the balloon (FIG. 14 and FIG. 15) and in thecenter of the balloon define radial spaces 20 ₁₋₄, 20 ₁₋₂, 20 ₂₋₃ and 20₃₋₄ between them (FIG. 14a). Each of the radial spaces are formed by apair of opposed radially and axially extending wall members 94 extendingbetween the outer wall of balloon 20 and the inner core catheter 3. Thedistal end of the balloon is attached to the inner core catheter 3 atthe attachment of the cone 2 and the proximal end of the balloon ismolded to the more proximal portion of the inner core catheter 3 atpoint 18.

[0134] The thermal transfer device 60C further includes a frame assembly62C comprising four pairs of scaffolding wires 21, each wire having oneend attached to the introducing conus 2, another end molded into theouter core catheter 8 at point 9 and a central region connected toballoon 20 by extending through passages 5 a.

[0135] The stent-capturing device 70C comprises capturing wire fingers23 situated in respective radial spaces 20 ₁₋₄, 20 ₁₋₂, 20 ₂₋₃ and 20₃₋₄, each of which has one end attached to inner core catheter 3 andextends at an angle from the core catheter 3 between adjacent pairs ofradial sectors 201 ₁-20 ₄. A pair of connecting bars or bridging members22 a, 22 b extend between each pair of the opposed walls 94 and capturesa respective one of the capturing wires between them. As seen in FIG.16, when the balloon 20 is collapsed, each capturing wire finger 23 willbe engaged by the bridging member 22 a to automatically close thecapturing wire finger. On the other hand, when the balloon is expanded,each capturing wire finger 23 will be engaged by a bridging member 22 bto automatically open the capturing wire finger.

[0136] In order to circulate thermal transfer fluid through the chamberof balloon 20 in the first version of the third embodiment shown inFIGS. 13-16, inflow and outflow channels 14 and 13 are formed in theinner core catheter 3 having inflow and outflow ports 14 a and 13 a.

[0137]FIG. 25 shows the proximal end of the system of the first versionof the third embodiment shown in FIGS. 13-16 outside the patient, wherethe stent receiving sheath 11 has a side arm port 28 for flushing ofheparinized saline to prevent thrombus formation in the space betweenthe stent receiving sheath 11 and the outer core catheter 8. The outercore catheter 8 has a side port 28 for flushing of heparinized saline toprevent thrombus formation between the outer core catheter 8 and theinner movable core catheter 3, which itself has two side ports: one port29 for inflow of solution/gas into the inflow channel 14 of balloon 20and the other port 26 for outflow of a solution/gas from the outflowchannel 13, which is connected to the bag (not shown).

[0138] Referring to FIG. 17, FIG. 18, FIG. 19 and FIG. 20, the proximalend of the cloverleaf balloon 20 is attached to the outer core catheter8 at point 18 a. A second version of the third embodiment of theinvention is illustrated wherein the space between the outer corecatheter 8 and the movable core catheter 3 is used as an inflow channel25 for infusion of a thermal solution or gas into the balloon. Themovable core 3 has a central lumen for the guidewire 1 and channel 13for outflow of circulating thermal solution or gas. The rest of thedesign of this system is identical to the system of FIGS. 13-16.

[0139] FIGS. 20D-F illustrate a modification of the system wherein bothinflow and outflow channels 25 and 31 are provided through the spacedefined between the outer core catheter 8 and the movable core catheter3. The channels are separated by two dividing partitions that extendalong the entire length of the catheter.

[0140]FIG. 26 illustrates the proximal end of the system shown in FIGS.17-20 outside the patient, where the stent receiving sheath 11 has aside arm port 28 for flushing of heparinized saline to prevent thrombusformation in the space between the stent receiving sheath 11 and theouter core catheter 8. The outer core catheter 8 has a side arm port 27for infusion of a thermal fluid into the cloverleaf type balloon. Themovable core catheter 3 has an opening of an outflow channel 26 from theballoon and is connected to the collecting bag (not shown). A stop-cockis placed on the outflow channel 26 and is closed in cases of performinga balloon angioplasty.

[0141] Referring to FIG. 21 a clinical scenario of primary stentdeployment using the cloverleaf balloon system of FIGS. 17-20 is shownfor deploying a stent made of a shape memory allow having a transitiontemperature at or below body temperature. The collapsed stent coveredwith the outer sheath is positioned inside the area of focal narrowingof the vessel under fluoroscopic guidance (FIG. 21a). The sheath is thenwithdrawn exposing the collapsed mounted stent and the infusion of acold solution or gas is started immediately to control expansion of thestent (FIG. 21b). The collapsed stent is secured with the capturingwires or fingers , which together with the local cooling preventpremature expansion of the device. When the position of the system isprecisely adjusted to the desired location under fluoroscopic guidance,the infusion of a cold thermal fluid is stopped and the metallic frameassembly is expanded by moving forward the outer core catheter along thefixed movable core (FIG. 21c). This allows natural heating of the stentto body temperature and its expansion to the original shape and diameterinside the area of stenosis, providing high radial force on the walls ofthe vessel and opening the narrowed region of the vessel. The primarystent deployment can be supplemented with a balloon angioplasty underhigh pressure, which is achieved by closing the outflow channel 13 andinfusion of a diluted contrast material via the inflow channel (FIG.21d). The pressure inside the balloon is regulated by the manometerattached to the inflow port outside the patient. The balloon is thendeflated by stopping the infusion of the contrast material and openingthe outflow channel, as well as collapsing the metallic frame by movingthe movable core catheter forward along the fixed outer core catheter(FIG. 21e). This maneuver also causes the stent-capturing fingers orwires to slide out of the cellular spaces in the stent, releasing thestent from the physical restraint (FIG. 21e). The collapsed metallicframe and deflated balloon are then withdrawn back into the sheath andthe entire system is removed from the body, leaving the stent in place(FIG. 21f).

[0142] The same system can be used for primary deployment of stentshaving a temperature of transformation higher than body temperature.Such stent is mounted on the balloon and delivered into the desiredlocation inside the body covered with an outer sheath. It is thenunsheathed, but does not expand until infusion of a warm solution athigher than body temperature is started via the inflow channel. Theframe is then opened and the stent expands to its original shape anddiameter, which it maintains after discontinuation of the infusion of awarm solution. The primary stent deployment can be supplemented with aballoon angioplasty in the same fashion as described above. The frame isthen collapsed by moving the movable core forward along the fixed outercatheter, which provides sliding of the capturing wires out of thestent. The stent stays in place, exhibiting persistent radial force onthe walls of the vessel or other tubular organ. The delivery system isthen safely removed from the body.

[0143] Referring to FIG. 22 the steps of 2-way shape memory stentretrieval with the cloverleaf balloon design are shown. The closedsystem is introduced and positioned inside the stent, which has to beremoved (FIG. 22a). The outer sheath is then withdrawn back and assumesa flared configuration after detaching from the introducing conus (FIG.22b). The metallic frame opens by advancing the outer core catheteralong the fixed movable core and the cold thermal transfer fluid isinfused into the balloon to cool the stent to the desired temperature,which is lower for stents with the first transition temperature at orbelow body temperature and higher (but still lower than bodytemperature) for stents with the first transition temperature above bodytemperature (FIG. 22c). The outer core catheter 8 is then moved backwhile the movable core catheter 3 remains fixed in the same position,stretching the frame and collapsing the balloon. The stent, or at leastits proximal end, collapses with reduction in diameter of the frame 62c, while the stent-capturing wires 23 stay open nearly touching thevessel wall (FIG. 22d). The stent, or at least its proximal end,collapses over the stent capturing wires 23, which protrude through thecells of the stent. The stent capturing wires 23 remain open until theymeet the cross bars 22 bridging the spaces between the sectors 20 ₁-20 ₄of balloon 20. Further stretching of the frame 62C causes closure of thecapturing wires 23 over the balloon 20 with the stent, or its proximalportion, caught between the capturing wires 23 and the balloon 20 (FIG.22e). At this point the stent is easily drawn into the receiving sheath(FIG. 22f). The next step is complete removal of the recovered stentfrom the body (FIG. 22g) or adjustment of its position while the stentis still in the collapsed state within the sheath with subsequentre-deployment into the desired location, using the same sequence of thesteps for primary stent deployment described above.

[0144] The above described methods prevent any motion of the deliverysystem during deployment. The entire stent uniformly expands at the sametime inside the area of narrowing, exerting radial force on the diseasedwall of the vessel and restoring the normal lumen and flow. All currentself-expanding stents have to be unsheathed gradually, exposingimmediately expanding small segments of the device at a time. Persistentpulling back of the sheath during opening of the stent inside the vesselcan cause slight forward or backward motion of the device, potentiallyleading to misplacement of the stent proximal or distal to the area ofinterest. This problem is eliminated by the system described above.

[0145] Referring to FIG. 23, another device 70D for capturing the stentis illustrated. As the stent is cooled by the thermal transfer device60, and partially collapses, it is grabbed on the balloon by a snareloop 30. The loose snare loop 30 is advanced around the partiallycollapsed stent and then tightens into a smaller loop by sliding thethin catheter over it. This maneuver securely fixes the stent to theframed balloon and promotes further mechanical collapse of the stent foreasy insertion into the outer sheath 11.

[0146] While the embodiments of the invention described above allutilize heated or cooled fluid circulating through the balloon chamberto transfer heat to or from the stent, the thermal transfer device maycomprise means for directly heating the heat transfer surface of thedevice.

[0147]FIG. 27 illustrates a solid balloon system with multiple heatingelectrical resistance wires 34 provided on the surface of the balloon 12to provide direct heating of the stent when an electrical current ispassed through the wires. The wires 34 are connected to an electricalsource outside the patient. This system can be beneficial for thedeployment of stents having transition temperatures above bodytemperature.

[0148] Referring to FIG. 28, the outer surface of the solid balloon 12is provided with an electromagnetic coil 48, which is heated bygeneration of an electrical current from application of an externalmagnetic field. The electromagnetic balloon can be used for deploymentof stents having transition temperatures higher than body temperature bydirect heating of the stent or by heating fluid injected into theballoon. The same system can be used for retrieval or repositioning ofthe stents with transformation temperatures greater than bodytemperature by infusing a cooling solution/gas into the balloon.

[0149] While the first, second and third embodiments of the inventiondescribed above utilize thermal transfer fluid which is heated or cooledat the proximal end of the catheter assembly outside the body, othertechniques for heating the thermal fluid may be employed.

[0150]FIG. 29 illustrates a solid balloon system with an electromagneticcoil 49 inside the balloon (as opposed to outside the balloon as shownin FIG. 28) to provide heating of the fluid in the balloon chamber afterapplication of an external magnetic field. It is applicable for thedeployment, repositioning or retrieval of the stents with firsttransformation temperatures higher than body temperature.

[0151]FIG. 30 illustrates a thermal transfer device provided withmultiple optic fibers 47 inside the balloon for heating of thecirculating fluid by a laser beam, which is connected to a sourcegenerator system on the proximal end outside the patient. The system canbe used for the deployment, repositioning or retrieval of stents withfirst transformation temperatures higher than body temperature.

[0152] Referring to FIG. 31, optic fibers 46 are situated on the outersurface of the balloon and can be used for direct heating of the mountedstent or for heating of fluid circulating inside the balloon. The systemcan be used for the deployment, repositioning or retrieval of the stentswith transition temperature higher than body temperature.

[0153]FIG. 32 demonstrates another system with an ultrasound probe 51inside the balloon, which provides fast heating of the circulating fluidfor the deployment of stents with transition temperatures higher thanbody temperature. An ultrasound generator is connected to the system onthe proximal end outside the patient. The system can be also used forrepositioning or retrieval of the same stents by circulation of coolingthermal fluid inside the balloon.

[0154] All currently available and all future stents and stent-graftsmade from Nitinol or other materials with shape memory capabilities canbe delivered with the above described systems and after training orheat/mechanical treatment can demonstrate second way memory effect, andcan be retrieved from the body or repositioned into the desired locationby using the systems that are described in this patent.

[0155] Obviously, numerous variations of the present invention arepossible within the scope of the claims appended hereto. Accordingly,the invention may be practiced otherwise than as specifically describedherein.

We claim:
 1. A method of delivering a shape memory stent having atransition temperature at or below body temperature to, and deployingthe stent at a diseased tubular area in the body, comprising the stepsof: mounting the shape memory stent in a collapsed condition on athermal transfer device coupled to a catheter assembly, said thermaltransfer device including a chamber having an outer transfer thermalwall, such that the heat transfer wall is in local heat transferrelationship with the stent; delivering the stent in said collapsedcondition on said thermal transfer device to a region of the diseasedtubular area in the body; infusing a flow of cooling thermal fluid intosaid chamber, commencing at least as early as the time the stent in itscollapsed condition on the thermal transfer device has been delivered toa region of the diseased tubular area; if necessary, adjusting theposition of the stent in said collapsed condition on said thermaltransfer device in said narrowing tubular area; controlling theexpansion of said stent into supporting engagement with the wall of thediseased tubular area by adjusting the temperature and/or rate of theinflow of cooling thermal fluid into said chamber.
 2. The method ofclaim 1 further including the steps of, during said delivery step,shielding the collapsed stent on the thermal transfer device to at leastpartially inhibit the heating of the stent to body temperature by thesurrounding body tissue during said delivery step; and exposing thecollapsed stent to the body upon substantial completion of said deliverystep; and wherein said infusing step commences upon substantialcompletion of said delivery step and upon exposing of the collapsedstent to the body.
 3. The method of claim 2 wherein said shielding stepcomprises covering said collapsed stent on the thermal transfer devicewith a movable outer sheath situated in a forward position and formingpart of said catheter assembly during delivery, and said exposing stepcomprises withdrawal of said outer sheath to a retracted position. 4.The method of claim 1 wherein said in fusing step commences at thesubstantial commencement of said delivery step.
 5. The method of claim 1including the further steps of, releaseably capturing said stent to saidcatheter assembly at the time of said mounting step; maintaining saidcapture of said stent to said catheter assembly during said deliverystep; maintaining said capture of said stent to said catheter assemblyduring at least a part of said deploying step; and releasing said stentfrom capture to said catheter assembly after completion of at least apart of said deploying step.
 6. The method of claim 5 wherein said stepof releasing said stent from capture to said catheter assembly commencessubstantially upon completion of said deploying step.
 7. The method ofclaim 5 wherein said catheter assembly comprises a stent-capturingsheath having a distal end; at least one hook member affixed to saiddistal end of said stent-capturing sheath; and an outer sheath having adistal end movably positioned over said stent-capturing sheath; andwherein said releasing step comprises moving said outer sheath withrespect to said stent-capturing sheath whereupon said distal end of saidouter sheath cooperates with said at least one hook member to move thesame to release said stent.
 8. The method of claim 5 wherein saidthermal transfer device comprises a balloon expandable and collapsiblebetween expanded and collapsed conditions.
 9. The method of claim 8wherein subsequent to the step of deploying said stent into supportingengagement with the wall of the diseased tubular area, performing aballoon angioplasty by expanding said balloon to engage said deployedstent and forcefully urge said stent against the wall of the diseasedtubular area.
 10. The method of claim 9 wherein said catheter assemblycomprises inflow passage means through which cooling thermal fluid isinfused into said chamber during said infusing step and outflow passagemeans for providing a controllable outflow of cooling thermal fluid fromsaid chamber, and wherein said step of performing an angioplasty byexpanding the balloon comprises expanding the balloon by inflation underpressure by infusing fluid under pressure into said chamber andcontrolling the outflow of the fluid from said chamber to inflatinglyexpand said balloon under internal pressure into an expanded conditionto engage said deployed stent and forcefully urge said stent against thewall of the narrowing tubular area.
 11. The method of claim 10 whereinsaid step of performing an angioplasty further comprises, in conjunctionwith said inflation of the balloon, actuating mechanical means coupledto said balloon for mechanically expanding the balloon into an expandedcondition to engage said deployed stent and forcefully urge said stentagainst the wall of the diseased tubular area.
 12. The method of claim 8wherein said releasing step comprises releasing said stent from captureto said catheter assembly by means activated by expansion of saidballoon.
 13. The method of claim 11 wherein said catheter assemblycomprises an inner core catheter and a relatively movable outer corecatheter situated over said inner core catheter, said outer corecatheter having a distal end which is situated proximally of the distalend of said inner core catheter so that projecting portion of said innercore catheter extends beyond said distal end of said outer corecatheter, and a wire frame comprising a plurality of wires, each wirehaving one end affixed to a distal end of said projecting portion ofsaid inner core catheter, another end affixed to the distal end of saidouter core catheter, and a mid-region attached to said expandableballoon; and wherein said actuating step comprises moving said inner andouter core catheters with respect to each other to bend said wires in anoutward direction and thereby expand said balloon.
 14. A method ofdelivering a shape memory stent having a transition temperature at orbelow body temperature to, and deploying the stent at, a diseasedtubular area within the body, comprising the steps of: mounting theshape memory stent in a collapsed condition on an inflatable balloon ina collapsed condition coupled to a catheter assembly, said balloonhaving a chamber and having an outer heat transfer wall, such that theheat transfer wall is in local heat transfer relationship with thestent; delivering the stent in said collapsed condition on saidcollapsed balloon to a region of the diseased tubular area in the body;commencing a circulating flow into and from said chamber of said balloonat least as early as the time the stent in its collapsed condition onthe collapsed balloon has been delivered to a region of the diseasedtubular area; said circulating flow comprising infusing a flow ofcooling thermal fluid from a proximal end of the catheter assembly intosaid chamber of said balloon, and withdrawing a flow of cooling thermalfluid from said chamber of said balloon to the proximal end of thecatheter assembly; if necessary, adjusting the position of the stent insaid collapsed condition on said collapsed balloon in said diseasedtubular area; controlling the expansion of said stent into supportingthe engagement of the wall of the diseased tubular area by adjusting thetemperature and/or rate of the inflow of cooling thermal fluid into saidchamber.
 15. The method of claim 14 wherein subsequent to the step ofdeploying said stent into supporting engagement with the wall of thediseased tubular area, performing a balloon angioplasty by expandingsaid balloon into an expanded condition to engage said deployed stent,and forcefully urging said stent against the wall of the diseasedtubular area; and wherein said catheter assembly comprises inflowpassage means through which cooling thermal fluid is infused into saidchamber during said infusing step and outflow passage means forproviding a controllable outflow of cooling thermal fluid from saidchamber, and wherein said step of performing an angioplasty by expandingthe balloon comprises expanding the balloon by inflation under pressureby infusing fluid under pressure into said chamber and controlling theoutflow of the fluid from said chamber to inflatingly expand saidballoon under internal pressure into an expanded condition to engagesaid deployed stent and forcefully urge said stent against the wall ofthe narrowing tubular area.
 16. The method of claim 15 wherein said stepof performing an angioplasty further comprises, in conjunction with saidinflatingly expanding the balloon, actuating mechanical means coupled tosaid balloon for mechanically expanding the balloon into an expandedcondition to engage said deployed stent and forcefully urge said stentagainst the wall of the diseased tubular area.
 17. The method of claim16 wherein said catheter assembly comprises an inner core catheter andrelatively movable outer core catheter situated over said inner corecatheter, said outer core catheter having a distal end which is situatedproximally of the distal end of said inner core catheter so thatprojecting portion of said inner core catheter extends beyond saiddistal end of said outer core catheter, and a wire frame comprising aplurality of wires, each wire having one end affixed to a distal end ofsaid projecting portion of said inner core catheter, another end affixedto the distal end of said outer core catheter, and a central regionattached to said expandable balloon; and wherein said actuating stepcomprises moving said inner and outer core catheters with respect toeach other to bend said wires in an outward direction and thereby expandsaid balloon.
 18. The method of claim 14 including the further steps of,releasably capturing said stent to said catheter assembly at the time ofsaid mounting step; maintaining said capture of said stent to saidcatheter assembly during said delivery step; maintaining said capture ofsaid stent to said catheter assembly during at least a part of saiddeploying step; and releasing said stent from capture to said catheterassembly after completion of at least part of the deployment step. 19.The method of claim 18 wherein said releasing step comprises releasingsaid stent from capture to said catheter assembly by means activated byexpansion of said balloon.
 20. The method of claim 18 wherein said stepof releasing said stent from capture to said catheter assembly commencessubstantially upon completion of said deploying step.
 21. The method ofclaim 18 wherein said catheter assembly comprises a stent-capturingsheath having a distal end; at least one hook member affixed to saiddistal end of said stent-capturing sheath; and an outer sheath having adistal end movably positioned over said stent-capturing sheath; andwherein said releasing step comprises moving said outer sheath withrespect to said stent-capturing sheath whereupon said distal end of saidouter sheath cooperates with said at least one hook member to move thesame to release said sheath.
 22. A method of delivering a shape memorystent having a transition temperature greater than body temperature to,and deploying the stent at, a diseased tubular area within the body,comprising the steps of: mounting the shape memory stent in a collapsedcondition on a thermal transfer device coupled to a catheter assembly,said thermal transfer device including a chamber having thermal transferwall, such that the heat transfer wall is in local heat transferrelationship with the stent; delivering the stent is said collapsedcondition on said thermal transfer device to a region of the diseasedtubular area in the body; controlling the expansion of said stent intosupporting engagement with the wall of the diseased tubular area byinfusing a flow of heating thermal fluid into said chamber, commencingonly after the time the stent in the collapsed position on the thermaltransfer device has been delivered to a region of the diseased tubulararea.
 23. A method of delivering a shape memory stent having atransition temperature at or below body temperature to, and deployingthe stent at, a diseased tubular area in the body comprising the stepsof: mounting the shape memory stent in a collapsed condition on aninflatable balloon in a collapsed condition coupled to a catheterassembly, said balloon having a chamber having an outer thermal transferwall, such that the thermal transfer wall is in local heat transferrelationship with the stent; delivering the stent in said collapsedcondition on said collapsed balloon to a region of the narrowing tubulararea in the body; commencing a circulating flow into and from saidballoon at least as early as the time the stent in its collapsedcondition on the collapsed balloon has been delivered to a region of thediseased tubular area, said circulating flow comprising an inflow ofcooling thermal fluid from a proximal end of the catheter assembly intosaid chamber of said balloon, and an outflow from the chamber of saidballoon to the proximal end of the catheter assembly; if necessary,adjusting the position of the stent in said collapsed condition on saidballoon in said diseased tubular area; controlling the expansion of thestent into supporting engagement with the wall of the diseased tubulararea by adjusting the rate and/or the temperature of the inflow ofcooling thermal fluid into said chamber; and during said controlledexpansion step, at least partially expanding the balloon.
 24. The methodof claim 23 wherein said step of expanding the balloon comprisescontrolling a circulating flow of fluid to and from the chamber of saidballoon.
 25. The method of claim 24 wherein said step of controlling thecirculating flow comprises controllably occluding said outflow from saidchamber.
 26. The method of claim 24 wherein said expansion fluidcomprises said thermal transfer fluid.
 27. The method of claim 24wherein said step of expanding the balloon comprises expanding a frameassembly on said catheter assembly and to which said balloon isattached.
 28. The method of claim 27 wherein the catheter assemblycomprises an inner core catheter and a relatively moveable outer corecatheter situated over said inner core catheter, said outer corecatheter having a distal end which is situated proximally of the distalend of said inner core catheter so that a projecting portion of saidinner core catheter extends beyond said distal end region of said outercore catheter, and wherein said frame assembly comprises a plurality ofwires, each wire having one end fixed to a distal end of said projectingportion of said inner core catheter, another end fixed to the distal endof said outer core catheter, and a central region attached to saidexpandable balloon.
 29. The method of claim 23 wherein subsequent to thestep of deploying said stent into supporting engagement with the wall ofthe narrow tubular area, performing a balloon angioplasty by expandingsaid balloon into an expanded condition to engage said deployed stentand forcefully urge said stent against the wall of a narrow tubulararea.
 30. The method of claim 29 wherein said step of performing anangioplasty by expanding the balloon comprises expanding the balloon byinflation under pressure by infusing a fluid under pressure into saidchamber of said balloon and restricting the outflow of the fluid fromsaid chamber.
 31. The method of claim 30 wherein said catheter assemblycomprises an expandable frame assembly to which said balloon is attachedto said catheter assembly, and wherein said step of performing anangioplasty further includes expanding said frame assembly on thecatheter assembly.
 32. The method of claim 23 wherein during saidmounting step, releaseably capturing said stent in said collapsedcondition to said catheter assembly by capturing means moveably affixedto said catheter assembly and coupled to said balloon; and wherein saidstep of expanding the balloon during deployment causes movement of saidcapturing means to maintain connection between said catheter assemblyand said stent as said stent expands; and wherein subsequent todeployment, releasing said capturing means from said stent by collapsingsaid balloon.
 33. A method of delivering a shape memory stent to, anddeploying the stent at, a diseased tubular area in the body, comprisingthe steps of: mounting a stent in a collapsed condition on a thermaltransfer device coupled to a catheter assembly, said thermal transferdevice including a thermal transfer surface such that the thermaltransfer surface is in local heat transfer relationship with the stent;delivering the stent in its collapsed condition on the thermal transferdevice to a region of the diseased tubular area in the body; afterdelivery, adjusting the temperature of the thermal transfer surface toadjust the temperature of the stent in local thermal transferrelationship to control the expansion of said stent to an expandedcondition whereupon the stent is deployed.
 34. The method of claim 33wherein the shape memory stent has a transition temperature at or belowbody temperature, and wherein said temperature adjusting step comprisesraising the temperature of the thermal transfer surface from atemperature below body temperature to allow the temperature of the stentto warm naturally to body temperature.
 35. The method of claim 33wherein the shape memory stent has a transition temperature above bodytemperature, and wherein said temperature adjusting step comprisesraising the temperature of the thermal transfer surface from bodytemperature to heat the stent to at least the transition temperature.36. The method of claim 33 wherein said temperature adjusting stepcomprises adjusting the temperature and/or rate of inflow of coolingthermal fluid into a chamber of said thermal transfer device.
 37. Themethod of claim 36 wherein said transfer device includes electricalheating wires in the chamber and said temperature adjusting stepcomprises adjusting the current flow through the heating wires.
 38. Themethod of claim 36 wherein said temperature adjusting step comprisesdirecting ultrasonic energy into the chamber.
 39. The method of claim 36wherein said temperature adjusting step comprises directing laser energyinto the chamber.
 40. The method of claim 33 wherein said temperatureadjusting step comprises directly controlling the temperature of thethermal transfer surface.
 41. The method of claim 40 wherein the thermaltransfer surface includes conductive heating wires and wherein said stepof directly controlling the temperature of the thermal transfer surfacecomprises adjusting the current flowing through said heating wires. 42.The method of claim 40 said step of directly controlling the temperatureof the thermal transfer surface comprises directing laser energy ontosaid thermal transfer surface.
 43. The method of claim 36 wherein saidinflow of thermal fluid comprises circulating thermal fluid from theproximal end of the catheter assembly into the chamber and from thechamber to the proximal end of the catheter assembly.
 44. The method ofclaim 33 including the further step of capturing the stent to thecatheter assembly during delivery, and releasing the stent from thecatheter assembly during expansion or upon completion of expansion. 45.The method of claim 33 wherein at least as early as completion ofdelivery and prior to the deployment, said step of adjusting thetemperature of the thermal transfer surfaces comprises cooling thethermal transfer surface.
 46. A method of capturing a two-way shapememory stent having first and second transition temperatures which isalready deployed in supporting engagement with a vessel wall at a firstposition for repositioning or retrieval comprising the steps of:providing an expandable and collapsible thermal transfer device in acollapsed condition on a catheter assembly, said expandable thermaltransfer device including a chamber having a thermal transfer wall;introducing said expandable thermal transfer device in its collapsedcondition on said catheter assembly into the lumen of the deployedstent; expanding the expandable thermal transfer device until itsthermal transfer wall is in local thermal transfer relationship with thedeployed stent; circulating a cooling thermal fluid from a proximal endregion of said catheter assembly into said chamber of said expandablethermal transfer device and from said chamber of said thermal transferdevice to said proximal end region of said catheter assembly to therebycool said deployed stent in local thermal transfer relationship withsaid thermal transfer wall to cause the temperature of the stent todecrease to or below the second transition temperature to thereby becomeat least partially collapsed, soft and pliable; capturing said at leastpartially collapsed and softened stent by stent-capturing means tocapture the stent to the catheter assembly.
 47. The method of claim 46wherein said expandable and collapsible thermal transfer devicecomprises a balloon.
 48. The method of claim 46 wherein said step ofexpanding said thermal transfer device comprises actuating a mechanicalframe assembly at said distal end of said catheter assembly coupled tosaid thermal transfer device until said heat transfer wall of saidthermal transfer device is in local thermal transfer relationship withsaid deployed stent.
 49. The method of claim 48 wherein said catheterassembly comprises an inner core catheter and a relatively movable outercore catheter situated over said inner core catheter, said outer corecatheter having a distal end which is situated proximally of the distalend of said inner core catheter so that a projecting portion of saidinner core catheter extends beyond said distal end of said outer corecatheter, and a wire frame comprising a plurality of wires, each wirehaving one end affixed to a distal end of said projecting portion ofsaid inner core catheter, another end affixed to the distal end of saidouter core catheter, and a central region attached to said expandableballoon; and wherein said actuating step comprises moving said inner andouter core catheters with respect to each other to bend said wires in anoutward direction and thereby expand said balloon.
 50. The method ofclaim 46 including the further step of partially collapsing said thermaltransfer device after said softened stent has been captured by saidstent capturing means and wherein said stent remains in constant localthermal transfer relationship with said thermal transfer wall of saidthermal transfer device.
 51. The method of claim 50 wherein saidcatheter assembly comprises an inner core catheter and a relativelymovable outer core catheter situated over said inner core catheter, saidouter core catheter having a distal end which is situated proximally ofthe distal end of said inner core catheter so that projecting portion ofsaid inner core catheter extends beyond said distal end of said outercore catheter, and a wire frame comprising a plurality of wires, eachwire having one end affixed to a distal end of said projecting portionof said inner core catheter, another end affixed to the distal end ofsaid outer core catheter, and a central region attached to saidexpandable balloon; and wherein said actuating step comprises movingsaid inner and outer core catheters with respect to each other to bendsaid wires in an outward direction and thereby expand said thermaltransfer device.
 52. The method of claim 48 wherein said thermal fluidcirculating step occurs at a low pressure during said balloon expansionstep.
 53. The method of claim 46 wherein said step of cooling saiddeployed stent is conducted to cause one portion of the stent tocollapse before collapse of the entire stent.
 54. The method of claim 46comprising the further step of, after capturing the stent, retrievingthe stent from the body.
 55. The method of claim 54 wherein saidcatheter assembly includes a stent-receiving sheath, and wherein saidstep of retrieving said stent from the body comprises the steps of:fully collapsing said thermal transfer device; positioning the softenedstent into said stent-receiving sheath; and withdrawing the catheterassembly from the body.
 56. The method of claim 46 comprising thefurther step of, after capturing the stent, repositioning the stent in asupporting engagement with a vessel wall at a second position.
 57. Themethod of claim 56 wherein said catheter assembly includes astent-receiving sheath, said two-way shape memory stent has a firsttransition temperature at or below temperature and wherein said step ofrepositioning said stent at a second position comprises the steps of:fully collapsing said thermal transfer device; positioning the softenedstent into said stent-receiving sheath into local thermal transferrelationship with said thermal transfer wall of said thermal transferdevice; repositioning the catheter assembly in the body so that saidstent, situated in said stent-receiving sheath, is repositioned at saidsecond position; and exposing the stent from within the stent-receivingsheath to expose the stent to body temperature, whereupon said stent isheated by the body and expands into supporting engagement with thevessel wall at said second position.
 58. The method of claim 56 whereinsaid step of repositioning said stent at a second position comprises,while maintaining circulation of said cooling thermal fluid,repositioning the catheter assembly in the body so that the stent isrepositioned at said second positioning, and terminating the circulationof the cooling thermal fluid.
 59. The method of claim 57 wherein saidstep of repositioning said stent comprises the further step of afterexposing the stent from the stent-receiving sheath, releasing the stentfrom the stent-capturing means to free the stent from the catheterassembly.
 60. The method of claim 56 wherein said catheter assemblyincludes a stent-receiving sheath, said two-way shape memory stent has afirst transition temperature greater than body temperature, and whereinsaid step of repositioning the stent at a second position comprises thesteps of: fully collapsing said thermal transfer device; drawing thesoftened stent into said stent-receiving sheath by said stent-capturingmeans into local thermal transfer relationship with said thermaltransfer wall of said thermal transfer device; repositioning thecatheter assembly in the body so that said stent situated in saidstent-receiving sheath is repositioned at said second position; exposingthe stent from the stent-receiving sheath; if necessary adjusting theposition of the system within the diseased area; circulating a heatingthermal fluid from a proximal end region of said catheter assembly intosaid chamber of said thermal transfer device and from said chamber ofsaid proximal end region of said catheter assembly to thereby heat saidstent in local thermal transfer relationship with said thermal transferwall to cause the temperature of the stent to increase to the firsttransition temperature to thereby expand into supporting engagement withthe vessel wall at the second position; and releasing the stent fromsaid capturing means.
 61. A method of capturing a two-way shape memorystent which is already deployed in supporting engagement with a vesselwall, for repositioning or retrieval comprising the steps of: providinga thermal transfer device on a catheter assembly, said thermal transferdevice having a thermal transfer surface; introducing the thermaltransfer device into the lumen of the deployed stent; positioning thethermal transfer device until the thermal transfer surface is in localthermal transfer relationship with the deployed stent; reducing thetemperature of the thermal transfer device to thereby cool said deployedstent in local heat transfer relationship with said thermal transfersurface to cause the temperature of the stent to decrease to or belowthe second transition temperature to thereby become at least partiallycollapsed, soft and pliable, and separate from the vessel wall and;capturing the at least partially collapsed and softened stent bystent-capturing means to capture the stent to the catheter assembly. 62.The method of claim 61 wherein said thermal transfer device isexpandable and collapsible, and wherein said thermal transfer device isintroduced into the lumen of the deployed stent in its collapsedcondition, and wherein said positioning step comprises expanding thethermal transfer device.
 63. The method of claim 61 including theadditional step of positioning the captured stent into an outer sheath.64. The method of claim 63 including the further step of removing theouter sheath containing the stent from the body to retrieve the stent.65. The method of claim 63 including the further step of repositioningthe outer sheath containing the stent at a new location in the vesseland deploying the stent at said new position.